1. Field of the Invention
Embodiments of the present invention relate to a method, medium, and apparatus controlling a hard disk drive, and more particularly, to a method, medium, and apparatus controlling a track seek of a hard disk drive, where the hard disk drive compensates for a gain distortion and a phase delay according to a sinewave acceleration trajectory.
2. Description of the Related Art
Recording and/or reproducing apparatuses, e.g., hard disk drives (HDDs), may include a plurality of magnetic transducers that may write and/or read data by sensing and/or magnetizing a magnetic field(s) of rotating media, e.g., disk(s). Data may be stored in a plurality of concentric tracks, with each of the concentric tracks potentially having disk and track numbers. Tracks having the same track number, in a plurality of disks, may be referred to as a cylinder. Hence, each track may also be defined by a cylinder number.
Transducers may typically be integrated within a slider incorporated into a head gimbal assembly (HGA) when the recording and/or reproducing apparatus is a HDD. Each HGA may be attached to an actuator arm, which may have a voice coil located adjacent to a magnetic assembly that makes up the voice coil motor. Hard disk drives typically include a controller and a driving circuit that supplies current to excite a voice coil motor. Thus, the voice coil motor may rotate an actuator arm and move transducers across the surface of a disk(s).
When data is written or read, the hard disk drive may execute a track seek control routine for moving transducers from one cylinder to another cylinder. During the track seek operation, a voice coil motor may be excited to move transducers over a disk surface to a new cylinder. A controller may control the current applied to the voice coil motor such that the transducers are accurately moved to the center of a track of a new cylinder, for example.
In such an operation, it may be preferable to minimize the time required to read or write data from or to a disk(s). Hence, in the track seek control routine, executed by the hard disk drive, transducers should be moved to a new cylinder within a period of time as short as possible. Also, the time required to stabilize an HGA should be minimized so that transducers can quickly write or read data and may be accurately located adjacent to a new cylinder.
Conventionally, transducers may be moved rapidly from one track to a target track by performing a track seek control using a square wave acceleration trajectory. Unfortunately, since a square wave involves a harmonic frequency with a high frequency component, the mechanical components or assemblies of the HGA are excited by the high frequency component causing the HGA to resonate. Accordingly, residual vibration creates auditory noise, undesired vibration, etc., and thus, there is an increase in the settling time and the whole seek time required to write or read data.
A conventional technique developed to solve this problem is a track seek control method using a sinewave acceleration trajectory. A track seek controller, using the sinewave acceleration trajectory, is advantageous in lessening vibration and noise. The track seek control method using the sinewave acceleration trajectory has been discussed in Japanese Patent Laid-Open Publication Nos. 2002-133799 (May 10, 2002), 1990-7506 (Jan. 12, 1990), 1998-241306 (Sep. 11, 1998), and Korean Patent Laid-Open Publication No. 2004-52273 (Jun. 23, 2004), for example.
FIG. 1 is a circuit diagram illustrating a conventional track seek control apparatus 100 using a sinewave acceleration trajectory. The track seek control apparatus 100 includes a sinewave trajectory producer 102, a notch filter 116, a voice coil motor (VCM) driver 126, a head gimbal assembly (HGA) 128, and a state estimator 104.
The track seek control apparatus 100 executes a track seek control routine to move a transducer to a target track that is a track seek distance XSK away from a first track. As defined below in Equation 1, the sinewave trajectory producer 102 may create a position y*(n), a velocity v*(n), and an acceleration a*(n) every sampling period ‘n’ according to the sinewave acceleration trajectory:
                              [                                                                                          X                    cos                                    ⁡                                      (                    n                    )                                                                                                                                            X                    sin                                    ⁡                                      (                    n                    )                                                                                ]                =                              [                                                                                cos                    ⁢                                                                                  ⁢                                          (                                                                        2                          ⁢                          π                                                                          N                          SK                                                                    )                                                                                                                                  -                      sin                                        ⁢                                                                                  ⁢                                          (                                                                        2                          ⁢                          π                                                                          N                          SK                                                                    )                                                                                                                                        cos                    ⁢                                                                                  ⁢                                          (                                                                        2                          ⁢                          π                                                                          N                          SK                                                                    )                                                                                                            sin                    ⁢                                                                                  ⁢                                          (                                                                        2                          ⁢                          π                                                                          N                          SK                                                                    )                                                                                            ]                    ⁡                      [                                                                                                      X                      cos                                        ⁡                                          (                                              n                        -                        1                                            )                                                                                                                                                              X                      sin                                        ⁡                                          (                                              n                        -                        1                                            )                                                                                            ]                                              (        1        )                                                                    a              *                        ⁡                          (              n              )                                =                                    K              A                        ⁢                          I              M                        ⁢                                          X                sin                            ⁡                              (                n                )                                                    ,                                                                      I          M                =                              2            ⁢            π            ⁢                                                  ⁢                          X              SK                                                          K              A                        ⁢                          T              SK              2                                                                                                                v            *                    ⁡                      (            n            )                          =                              K            A                    ⁢                      I            M                    ⁢                                                    T                SK                                            2                ⁢                π                                      ⁡                          [                              1                -                                                      X                    cos                                    ⁢                                                                          ⁢                                      (                    n                    )                                                              ]                                                                                                                y            *                    ⁡                      (            n            )                          =                              K            A                    ⁢                      I            M                    ⁢                                                    T                SK                                            2                ⁢                π                                      ⁡                          [                                                                                          T                      SK                                                              N                      SK                                                        ⁢                  n                                -                                                                            T                      SK                                                              2                      ⁢                      π                                                        ⁢                                                            X                      sin                                        ⁡                                          (                      n                      )                                                                                  ]                                                                      
To calculate values of a sine function and a cosine function for producing the sinewave acceleration trajectory, the sine function and the cosine function are sampled every sampling period ‘n’, stored in a ROM table, and then read from the ROM table every sampling period n.
Meanwhile, a sine function and a cosine function, at one phase, can be derived from a sine function and a cosine function at another phase. Values of the sine function and the cosine function during a first sampling period are stored in the ROM table to calculate values of the sine function and the cosine function during other sampling period n, using the top sine/cosine equation of Equation 1, thereby reducing the necessary size the ROM table.
Values of a sine function and a cosine function, with respect to representative frequencies, during a first sampling period are stored in the ROM table and can be determined by interpolation. The frequency corresponds to a track seek distance and a track seek time. The track seek distance determines the track seek time, i.e., the frequency of a sinewave signal.
In the above Equation 1, constants KA, IM, XSK, and TSK denote an acceleration constant, a maximum volume of current, a track seek distance, and a track seek time, respectively. The track seek time (or a track frequency) is calculated based on an idealized dual integrator model, current, and voltage with respect to the track seek distance, the notch filter 116, and the VCM driver 122 and stored in the ROM table.
Referring to FIG. 1, in this conventional system, an acceleration trajectory a, a velocity trajectory v, and a position trajectory y are obtained by Equation 1. A temporal axis is based on the track seek time TSK. Thus, supposing that the track seek time TSK is 1, the acceleration trajectory a, the velocity trajectory v, and the position trajectory y can be obtained by Equation 1. The track seek time TSK corresponds to a period of the sinewave acceleration trajectory a. Here, the transducer is moved to the track seek distance XSK during the track seek time TSK, producing the acceleration trajectory a.
The acceleration constant KA, the maximum volume of current IM, the track seek distance XSK, and the track seek time TSK are given by the following Equation 2.
                              T          SK                =                                                            2                ⁢                π                                                              K                  A                                ⁢                                  I                  M                                                      ⁢                          X              SK                                                          (        2        )            
Thus, here, Equation 2 indicates that the track seek time TSK is a root of the track seek distance XSK.
FIG. 2 illustrates the track seek distance XSK versus the track seek time TSK. The state estimator 104, thus, estimates an estimated position y(n) and an estimated velocity v(n) of transducers based on positions of transducers at previous sampling periods n−1, n−2, . . . , and at a present sampling period n.
A gray code recorded on a sector of the disk is used to obtain a track position, i.e., a track number and read by transducers moving over the a disk. The gray code read by transducers is provided to the state estimator 104.
Referring to FIG. 1, a VCM driving current u(n) applied to the notch filter 116 is determined by the following Equation 3.u(n)=a*(n)+Kv(v*(n)−v(n))+KvKp(y*(n)−y(n))  (3)
The VCM driving current u(n), derived from Equation 3, is applied to the VCM driver 106 through the notch filter 116 to reduce vibration and noise caused by a track seek. The notch filter 116 is designed to control a frequency resonance. In such a system, the notch filter 116 and the VCM driver 126 are expressed as a constant gain in order to avoid complexity in the design of the seek trajectory. The HGA 128 is made up of a VCM, an arm, a head, and a disk in which the arm is moved by current that causes the VCM to move the head to a particular position to read the track position written on the disk, which is expressed as a dual integrator model in order to avoid complexity in the design of the seek trajectory.
Meanwhile, when the transducers move using the track seek control apparatus 100, a gain distortion and a phase delay are caused by the notch filter 116 and the VCM driver 126. While the track seek, based on Equation 1, is controlled by a dual integrator model combining the notch filter 116, the VCM driver 126, and the HGA 128, an actual system including the notch filter 116, the VCM driver 126, and the HGA 128 is actually different from the ideal dual integrator model.
FIGS. 3A and 3B illustrate gain distortion and phase delay caused by the notch filter 116 and the VCM driver 126. Referring to FIG. 3A, curves 302 and 304 indicate gain characteristics of the notch filter 116 and the VCM driver 126, respectively, and a curve 306 indicates the entire gain characteristics of the notch filter 116 and the VCM driver 126. Low frequencies have an ideal gain characteristic, whereas higher frequencies, i.e., shorter track seek distances, generate greater gain distortion.
Referring to FIG. 3B, curves 312 and 314 indicate phase characteristics of the notch filter 116 and the VCM driver 126, respectively, and a curve 316 indicates the entire phase characteristics of the notch filter 116 and the VCM driver 126. Similarly, Low frequencies have ideal phase characteristics, whereas higher frequencies, i.e., shorter track seek distances, generate greater phase distortion.
The real-life gain distortion and the phase delay caused by the notch filter 116 and the VCM driver 126, thus, differentiate the real-life system from the ideal model, thereby preventing the transducers from moving along correct trajectories.
To correct for an error between the notch filter and the VCM driver, the track seek control method must use a high gain controller, i.e., a very sensitive controller, or it must be designed to pursue conservative standard trajectories, i.e., relatively slow trajectories. However, the conventional high gain controller causes noise and makes the whole system insecure, and accordingly, conventional standard trajectory designs cause track seek times to increase.